1. Field of the Invention
This invention concerns a copolyester fiber consisting of a copolyester with mainly C.sub.2 -C.sub.4 alkylene terephthalate units, poly(C.sub.2 -C.sub.4 alkylene glycol) units, and units derived from polyfunctional compounds (pentaerythritol and/or carboxy methylene phosphonic acid and/or carboxy ethylene phosphonic acid), as well as a process for synthesis of these copolyester fibers by esterification, subsequent precondensation and polycondensation of terephthalic acid with C.sub.2 -C.sub.4 alkylene glycol, poly(C.sub.2 -C.sub.4 alkylene glycol), and a polyfunctional compound as well as spinning the resulting polyester in the melt at spooling speeds of at least 3000 m/min.
2. Summary of the Related Art
Copolyester fibers are known. Examined German Patent No. 1,266,922 discloses a process for producing fibers by melt spinning a modified polyester of terephthalic acid or isoterephthalic acid or the dimethyl esters thereof, ethylene glycol, 0.05 to 4.0 mol % alkoxy polyalkylene glycol and 0.05 to 2.4 mol % of a polyhydroxy compound such as pentaerythritol. The fibers or filaments of this modified polyester are essentially free of discoloration.
U.S. Pat. No. 5,756,033 describes a process for producing POY fibers from a polyester containing approximately 150 to 2500 ppm carboxy ethylene phosphonic acid units. The polyester may also contain up to 10 wt % other co-monomers, including polyglycols with a molecular weight of less than 1000. This patent does not disclose any relationship to the dyeing properties of the fibers or how to optimize them.
U.S. Pat. No. 4,086,208 also describes a flame-retardant polyester containing at most 10 mol % polyethylene glycol units and at least 2500 ppm carboxy ethylene phosphonic acid units.
It is also known that fibers of polyesters can be pigmented with disperse dyes. However, there are technical problems associated with dyeing because it is difficult for the large molecules of the disperse dyes to penetrate and diffuse into the amorphous portions of the partially crystalline polyester. Fibers of unmodified polyethylene terephthalate are therefore dyed at temperatures above 120.degree. C. and under excess pressure. However, it is also possible to add organic chemicals that penetrate like plasticizers into the polyethylene terephthalate, causing it to swell and thus making it more readily accessible for dyes. A disadvantage of this, however, is that the added organic chemicals are usually toxic substances that cause severe wastewater pollution.
International Patent Application WO 92/13120 discloses fine, non-delustered fibers that can be dyed at atmospheric pressure without chemical additives, the fibers consisting of a polyethylene terephthalate containing 3.9 wt % polyethylene oxide and 0.175 wt % trimethylol propane which must not contain any delustering agents. A disadvantage of these fibers with regard to uniform spinnability is the high trimethylol propane content. In addition, most applications require delustered fibers.